Make use a more coherent use of filters and filters_meta in docst…

…rings

README_CFRAME_FORMAT.rst

@@ -60,12 +60,12 @@ The header contains information needed to decompress the Blosc chunks contained
       +-- [msgpack] int32
 
 The filter pipeline is stored next in the header. It contains 6 slots, one for each filter that can be applied. For
-each slot there is a byte used to store the filter code in `filter_codes` and an associated byte used to store any
-possible filter meta-info in `filter_meta`::
+each slot there is a byte used to store the filter ID in `filters` and an associated byte used to store any
+possible filter meta-info in `filters_meta`::
 
 
     |-45|-46|-47|-48|-49|-4A|-4B|-4C|-4D|-4E|-4F|-50|-51|-52|-53|-54|-55|-56|
-    | d2| X | filter_codes          |_f4|_f5| filter_meta           |   |   |
+    | d2| X | filters               |_f4|_f5| filters_meta          |   |   |
     |---|---|-------------------------------|-------------------------------|
       ^   ^                           ^   ^                           ^   ^
       |   |                           |   |                           |   +-- reserved

README_CHUNK_FORMAT.rst

@@ -40,7 +40,7 @@ Starting in Blosc 2.0.0, there is an extension of the header above that allows
 for encoding blocks with a filter pipeline::
 
   1+|-0-|-1-|-2-|-3-|-4-|-5-|-6-|-7-|-8-|-9-|-A-|-B-|-C-|-D-|-E-|-F-|
-    |     filter codes      | ^ | ^ |     filter meta       | ^ | ^ |
+    |     filters           | ^ | ^ |     filters_meta      | ^ | ^ |
                               |   |                           |   |
                               |   +- compcode_meta            |   +-blosc2_flags
                               +- user-defined codec           +-reserved
@@ -105,8 +105,8 @@ for encoding blocks with a filter pipeline::
 :cbytes:
     (``int32``) Compressed size of the buffer (including this header).
 
-:filter_codes:
-    (``uint8``) Filter code.
+:filters:
+    (``uint8``) Filter ID.
 
     :``0``:
         No shuffle (for compatibility with Blosc1).
@@ -121,11 +121,12 @@ for encoding blocks with a filter pipeline::
     :``4``:
         Truncate precision filter.
     :``5``:
-        User-defined filter.
+        Sentinel. IDs larger than this are either global registered or user-defined filters.
 
-    The filter pipeline has 6 reserved slots for the filters. They are applied sequentially to the chunk according
-    to their index in increasing order. The type of filter applied is specified by the `filter_code`. Each
-    `filter_code` has an associated field in `filter_meta` that can contain metadata about the filter.
+    The filter pipeline has 6 reserved slots for the filters IDs. They are applied sequentially
+    to the chunk according to their index (in increasing order). The type of filter applied is
+    specified by the ID. Each ID has an associated field in `filters_meta` that can contain metadata
+    about the filter.
 
 :udcodec:
     (``uint8``) User-defined codec identifier.
@@ -135,10 +136,10 @@ for encoding blocks with a filter pipeline::
 
     Metadata associated with the compression codec.
 
-:filter_meta:
-    (``uint8``) Filter metadata.
+:filters_meta:
+    (``uint8``) Filter metadata associated to each filter ID.
 
-    Metadata associated with the filter code.
+    Metadata associated with the filter ID.
 
 :blosc2_flags:
     (``bitfield``) The flags for a Blosc2 buffer.

blosc/blosc2.c

@@ -660,10 +660,10 @@ typedef struct blosc_header_s {
   int32_t blocksize;
   int32_t cbytes;
   // Extended Blosc2 header
-  uint8_t filter_codes[BLOSC2_MAX_FILTERS];
+  uint8_t filters[BLOSC2_MAX_FILTERS];
   uint8_t udcompcode;
   uint8_t compcode_meta;
-  uint8_t filter_meta[BLOSC2_MAX_FILTERS];
+  uint8_t filters_meta[BLOSC2_MAX_FILTERS];
   uint8_t reserved2;
   uint8_t blosc2_flags;
 } blosc_header;
@@ -739,12 +739,12 @@ int read_chunk_header(const uint8_t* src, int32_t srcsize, bool extended_header,
     // The number of filters depends on the version of the header. Blosc2 alpha series
     // did not initialize filters to zero beyond the max supported.
     if (header->version == BLOSC2_VERSION_FORMAT_ALPHA) {
-      header->filter_codes[5] = 0;
-      header->filter_meta[5] = 0;
+      header->filters[5] = 0;
+      header->filters_meta[5] = 0;
     }
   }
   else {
-    flags_to_filters(header->flags, header->filter_codes);
+    flags_to_filters(header->flags, header->filters);
   }
   return 0;
 }
@@ -775,11 +775,11 @@ static int blosc2_initialize_context_from_header(blosc2_context* context, blosc_
     /* Extended header */
     context->header_overhead = BLOSC_EXTENDED_HEADER_LENGTH;
 
-    memcpy(context->filters, header->filter_codes, BLOSC2_MAX_FILTERS);
-    memcpy(context->filters_meta, header->filter_meta, BLOSC2_MAX_FILTERS);
+    memcpy(context->filters, header->filters, BLOSC2_MAX_FILTERS);
+    memcpy(context->filters_meta, header->filters_meta, BLOSC2_MAX_FILTERS);
     context->compcode_meta = header->compcode_meta;
 
-    context->filter_flags = filters_to_flags(header->filter_codes);
+    context->filter_flags = filters_to_flags(header->filters);
     context->special_type = (header->blosc2_flags >> 4) & BLOSC2_SPECIAL_MASK;
 
     is_lazy = (context->blosc2_flags & 0x08u);
@@ -894,8 +894,8 @@ static int blosc2_intialize_header_from_context(blosc2_context* context, blosc_h
   if (extended_header) {
     /* Store filter pipeline info at the end of the header */
     for (int i = 0; i < BLOSC2_MAX_FILTERS; i++) {
-      header->filter_codes[i] = context->filters[i];
-      header->filter_meta[i] = context->filters_meta[i];
+      header->filters[i] = context->filters[i];
+      header->filters_meta[i] = context->filters_meta[i];
     }
     header->udcompcode = context->compcode;
     header->compcode_meta = context->compcode_meta;

include/blosc2/filters-registry.h

@@ -25,11 +25,13 @@ enum {
     BLOSC_FILTER_BYTEDELTA_BUGGY = 34,
     // buggy version. See #524
     BLOSC_FILTER_BYTEDELTA = 35,
-    //!< Byteshuffle + delta.  Sometimes this can represent an advantage over
+    //!< Byteshuffle + delta.  The typesize should be specified in the `filters_meta` slot.
+    //!<  Sometimes this can represent an advantage over
     //!< @ref BLOSC_SHUFFLE or @ref BLOSC_BITSHUFFLE.
     //!< See https://www.blosc.org/posts/bytedelta-enhance-compression-toolset/
     BLOSC_FILTER_INT_TRUNC = 36,
-    //!< Truncate int precision; positive values in `filter_meta` will keep bits; negative values will zero bits.
+    //!< Truncate int precision; positive values in `filters_meta` slot will keep bits;
+    //!< negative values will remove (set to zero) bits.
     //!< This is similar to @ref BLOSC_TRUNC_PREC, but for integers instead of floating point data.
 };
 

tests/test_schunk_header.c

@@ -76,8 +76,8 @@ static char* test_schunk_header(void) {
   mu_assert("err clevel", schunk->clevel == 3);
   mu_assert("err typesize", schunk->typesize == 4);
   mu_assert("err blocksize", schunk->blocksize == 1024 * cparams.typesize);
-  mu_assert("err filter_meta 1", schunk->filters_meta[0] = 23);
-  mu_assert("err filter meta 2", schunk->filters_meta[1] = 24);
+  mu_assert("err  1", schunk->filters_meta[0] = 23);
+  mu_assert("err filters_meta 2", schunk->filters_meta[1] = 24);
   mu_assert("err filters 4", schunk->filters[4] = BLOSC_DELTA);
 
   // Check that the chunks have been decompressed correctly